[Coco] Status update and your input on the Floppy Disk Controller emulator for the CoCo

[gene heskett]

On Wednesday, June 01, 2011 06:59:11 PM Steve Bjork did opine:

> Earlier this year, work start on a Floppy Disk Controller emulator for
> the CoCo. This device would plug into a CoCo and emulate the functions
> of the Western Digital Floppy Disk Controller and Floppy Disk Drive. In
> place of the Floppy media, the device would use a SDHC memory card to
> store the floppy disk data.
> 
> Since the device would emulate the WD1793 and the other components on
> the Tandy Floppy Disk controller, it will work with most color computer
> software without any software patches. (Even most copy protected
> software.)
> 
> At the last CoCoFest, I received a lot of helpful input on the device.
> Some of the ideas ranged from adding a Network interface to talk to a
> host computer to a video circuit for 256 colors. But the best suggestion
> was KIS (Keep It Simple) so the device could be designed and build in
> the shorted time possible.
> 
> With the fact that others are working on both USB and Network interfaces
> for the CoCo, there is no need for the FDC emulator to anything more
> than the FDC and SDHC memory card. There will be a PC program for
> transferring data to the SDHC card and back. You could even use
> DriveWire or CoCoNet to talk to Host PC and will using the FDC emulator.
> These options should handle any need to talk to a host PC for getting
> data to and from the device.
> 
> The current design uses two micro-controller. The first is a small, but
> very fast chip to emulate the WD1793 and Tandy logic of the FDC pak. The
> second micro-controller handles the track format and data information
> stored in the SDHC card. The total cost of both micro-controllers cost
> less than $10 in single unit quantities.
> 
> The FDC emulator will have a number of setup switches and LEDs for
> configuring and status information. The first four switches will be the
> disk write protect switches. (Much like the write protect tabs on a
> floppy disk.) An eight way switch is the Boot configuration selector to
> load one of eight different drive/disk configurations with an auto boot
> option. A special �write protect all� switch that will keep the SDHC
> from being wrote to even if the CoCo start running bad code. (Handy for
> writing test code.) The LEDs will display drive motor on and Access for
> of the four drives plus a SDHC write protected status and access lights.
> 
> In addition to the FDC emulator mode, the device can run in special
> transfer mode for maxim throughput to the SDHC card. The applications of
> this mode range from OS-9 drivers to John W. Linville�s CoCo Video
> Player.
> 
> With the basic design of the FDC emulator now locked down, the type of
> CoCo Floppy Disk Controllers needs to be addressed. Both Tandy FDC paks
> are for the most identical from the software point of view. But there
> are third party devices with a few changes here and there. The question
> is, are they compatible (on the software) to the Tandy FDC pak. If not,
> what changes would I need to support to make software designed for them
> to work on FDC emulator?
> 
> The next item is the drive select lines. The standard Tandy setup uses 4
> drive select lines to select drives 0 to 3. There was also a
> semi-standard of using drive 4 select line as the head select line for
> double sided drives. Are there any other configurations for the Drive
> Select lines than these two?
> 
> Thank you for your input,
> 
> Steve Bjork

There could be others Steve, but those two setups will cover well over 
99.99% of all the coco hardware.  I don't think I'd give it a huge amount 
of attention, nor research unless someone pops up and says 'I have 3 copies 
of so-and-so that actually work this way' followed by how their version 
works.

4!=15 variations, but the two you quoted are the only ones that make sense.

-- 
Cheers, Gene
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